Vacuum-type circuit interrupter



May 4, 1965 T. H. LEE ETAL VACUUM-TYPE CIRCUIT INTERRUPTER Filed Sept. 19, 1961 T/ME Inventors: Thomas H. Lee, Harold N. Schneider,

Mae :5

Their Attorney.

United States Patent 3,182,156 VACUUM-TYPE CIRCUIT INTERRUPTER Thomas H. Lee, Media, and Harold N. Schneider, Springfield, Pa., assignors to General Electric Company, a corporation of New York Filed Sept. 19, 1961, Ser. No. 143,176 18 Claims. (6i. 200-144) This application is a continuation-in-part of our application S.N. 769,215, filed October 23, 1958, and assigned to the assignee of the present application. This invention relates to an electric circuit interrupter of the vacuum type and, more particularly, to contact, or electrode, structure for such an interrupter.

Heretofore, the use of vacuum-type circuit interrupters in inductive alternating-current power circuits has been avoided largely because previously available vacuum interrupters have generated excessive overvoltages when interrupting currents below several hundred amperes in such circuits. The factor that has been responsible for these overvoltages is the tendency for vacuum interrupters to chop during low current interruptions. By chopping" is meant forcing the current to zero abruptly and prematurely before a natural current zero is reached. This abrupt change in current which accompanies chopping induces across any device in the circuit a voltage equal to I Z, Where I is the chopping current in amperes, i.e., the instantaneous current level at which chopping occurs, and Z is the surge impedance of the device in ohms. The surge impedance for inductive devices is usually quite high, e.g., on the order of thousands of ohms and even higher, and thus the overvoltages that are generated by a chopping current of only, say ten amperes, are usually excessive.

A solution to the above described chopping problem is disclosed and claimed in application S.N. 750,784, Lee et al., now Patent No. 2,975,256, filed July 24, 1958, and assigned to the assignee of the present invention. This solution involves using for the contacts of the vacuum interrupter particular materials that are capable of evolving in response to all instantaneous arcing currents above the maximum permissible chopping level a sufficient supply of vapor to maintain the are stable and to provide a pressure at least as great as the arc-constricting magnetic pressure of the are at its terminals.

Examples of contact material capable of performing in this manner where the maximum permissible chopping level is four amperes are tin, antimony, lead, zinc, bismuth, and suitable alloys thereof.

While many of these materials are capable of interrupting arcing currents of high magnitude, there are other materials, such as pure copper and silver, which, from an overall viewpoint, are more suited for highcurrent interrupting duty. Pure copper, for example, is capable of interrupting higher currents than most of the materials claimed in the Lee et a1. application, is less expensive and is mechanically stronger than most such materials and evolves less vapors in response to high-current arcs than most such materials. This latter factor tends to lengthen the life of the interrupter by lessening the likelihood of the interrupter insulation becoming harmfully coated by vapor condensate. The high chopping level of certain materials under low current interrupting conditions is not a significant disadvantage in high current interruption inasmuch as chopping in a vacuum arc appears to be a phenomena that is confined to low current arcs.

Thus, an object of our invention is to provide, for a vacuum interrupter, improved contact structure that is capable of utilizing for low-current interruptions a material having a low current-chopping level and is capable of utilizing for high-current interruptions a material which might be inferior from a chopping viewpoint but is superior from a high interrupting capacity viewpoint.

Another object is to provide, for a vacuum interrupter, improved contact structure which (1) is capable of limiting the maximum current-chopping level to a relatively low value in comparison to that Which is characteristic of refractory metals, (2) has a high resistance to contactwelding, and (3) has a current interrupting-ability much higher than that which is characteristic of refractory metals.

In carrying out our invention in one form, We provide a vacuum-type circuit interrupter which comprises a highly evacuated envelope. Within the envelope we provide electrode structure comprising juxtaposed first and second electrode regions of dissimilar conductive materials, the material of the first region having a substantially lower characteristic current-chopping level than the material of the second region. Substantially all of the arcs that the interrupter is to extinguish are initiated with one terminal located on said first region at the instant of arc-initiation. The first electrode region has sufficient surface area to cause the terminal for low current arcs to be maintained thereon until arc-extinction. Magnetic means is provided for driving arcs from their initiation point toward said second electrode region with a speed varying in accordance with the current being interrupted. The magnetic means acts to drive high current arcs at a sufiiciently high speed to locate the terminal of said high current arcs on the second region during a substantial portion of the arcing period. The magnetic means has insufiicient arc-motivating ability during low current interruptions to drive the terminal of low current arcs off of the first electrode region before arc-extinction.

For a better understanding of our invention reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a sectional view of a vacuum-type circuit interrupter comprising contact structure embodying one form of our invention.

FIG. 1a is an enlarged sectional View of a portion of the contact structure of FIG. 1.

FIG. 2 is an enlarged perspective view of one of the contacts of FIG. 1.

FIG. 3 is an enlarged perspective view of the other contact of FIG. 1.

FIG. 4 is :a graphic representation illustrating the above-described chopping phenomena.

FIG. 5 is a sectional view of a modified form of contact structure for use in connection with an interrupter of the type shown in FIG. 1.

FIG. 6 is a right-hand end view of the contact structure of FIG. 5.

FIG. 7 is a sectional view of still another modified form of contact structure for use in connection with an interrupter of the type shown in FIG. 1.

Referring now to the interrupter of FIG. 1, there is shown a highly evacuated envelope 10 comprising a casing 11 of suitable insulating material and a pair of metallie end caps 12 and 13 closing off the ends of the casing 11. Suitable seals 14 are provided between the end caps and the casing to render the envelope 1t vacuum-tight.

The pressure within the envelope it? under static conditions is preferably below 10- mm. of mercury. As is well known, at these low pressures, the vacuum has a very high dielectric strength because there are so few molecules of gas remaining in the envelope that electrons can travel across the various gaps between the high voltage parts of the interrupter with little probability of colliding with the gas molecules that are present. It is these collisions which are primarily responsible for ionization arsaree and resultant electrical breakdown. If pressures substantially higher than 1W mm. of mercury were to be utilized, then at least some of the interrupters potential breakdown paths would be longer than the average distance with which the electrons could travel without colliding with a gas molecule. This average distance is commonly called the mean free path. Only with pressures less than about mm. of mercury is there a reasonable assurance that the mean free path of an electron will be longer than the potential breakdown paths in the interrupter. It is only under this latter condition that one achieves, the high level of dielectric strength that is generally required in a commercial vacuum circuit interrupter.

Located within the envelope to is a pair of separable disk shape contacts 17 and lie shown in their engaged, or closed-circuit, position. The upper contact J] is a stationary contact suitably secured to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact i8 is a movable contact joined to a conductive operating rod 18a which is suitably mounted for vertical movement. The operating rod 18a projects through an opening in the lower end cap 13, and a flexible metallic bellows provides a seal about the rod 18a to allow for vertical movement of the rod without impairing the vacuuminside the envelope. As shown in FIG. 1, bellows 24} is sealingly secured at its respective opposite ends to the operating rod 18a and the end cap 13.

Coupled to the lower end of the operating rod Elba, we provide suitable actuating means (not shown) which is capable of driving the contact 18 downwardly out of engagement with the contact It? so as to open the interrupter and which is also capable of returning the contact 18 to its illustrated position soas to close the interrupter. In connection with these opening and closing operations, it is to be understood that the power circuit through the interrupter extends from end cap 12, through the parts 17a, 17, 18 and 18a. A circuit-opening operation will soon be explained in greater detail.

In the embodiment of FIG. 1, each contact is of a disk shape and has one of its major surfaces facing the other contact. The central region of each contact is provided with a recess 29 in this major surface, and an annular contact-making area 3'9 surrounds this recess. In each contact this contact-making area 30 is defined by the exposed surface of an annulus 31 which is integrally united with the remainder of the contact. FIG. 1a illustrates a suitable brazed joint 33 integrally uniting the annulus 31 and the remainder of the contact, as will soon be explained in greater detail. It is to be noted that only a portion of the exposed surface of the annulus 31 serves as a contact-making area inasmuch as the remainder of the exposed surface, designated sea, is chamfered or otherwise recessed so as to render it incapable of making contact with or engaging the other contact. Arcs will therefore be initiated radially inwardly of the surface Eda upon disengagement of contacts during an opening operation. Both the annulus 31 and the remainder of the contact are formed of conductive materials, but these materials are dissimilar and have different current-chopping characteristics, as will soon be explained in greater detail. Surrounding the. annulus 31, each contact has an annular surface 32, which is. hereinafter termed the arcrunning surface. This arc-running surface 32 extends from the outer periphery of the annulus 31 to the outer periphery of the contact disk 17 or 18. The exposed surface of the annulus 31 is referred to at various points hereinafter as a first electrode region, whereas the arc-running surface 32 is referred to hereinafter as a second electrode region.

The two annular contact-making areas 30 of the mating contacts 17 and t8 abut against each other when the contacts are in their closed position of FIG. 1, and are of such an internal diameter that the current flowing through the closed contacts is forced to follow a loop-shaped path L, as is indicated by the dot-dash lines of FIG. 1. This loop-shaped path has a magnetic effect which tends in a well-known manner to lengthen the loop. As a result, when the contacts are separated to form an arc between the areas 3%, the magnetic effect ofv the loop will impel the arc radially outward toward the arc-running surface 32.

To insure that the loop L has the proper configuration, it is important that the brazed joint between the annulus 31 and the body portion of the contact be properly located. More particularly, the brazed joint should be located at the back face of the annulus and preferably should extend at least across the region of the back face which radially aligns with the contact-making area 36. No brazing or other form of connection should be employed around the outer periphery of the annulus. By so confining the brazed joint, we insure that the loop L for the majority of the current is devoid of any radiallyinwardly bowed portion in the immediate region of the contact-making area St Such a radially-inwardly bowed portion would exert a magnetic force radially-inward and could thus interfere with the desired radially-outward movement of the are.

The speed at which the arc moves radially outward toward the arc-running surface 32 depends upon the magnitude of the arcing current and varies as a direct function of this arcing current. In other words, arcs of relatively high current magnitude move rapidly outward toward the arc-running surface 32, whereas arcs of relatively low current magnitude move at considerably lesser speeds than the high current arcs. The exposed surface 3%, 30a of the annulus 31 extends radially outward to such an extent that the terminal for all of those arcs.

carrying peak values of arcing current below several hundred amperes remains on the surface of the annulus 31. In other words, the speed at which such low currrent arcs move radially outward is insufficient to carry the arc terminal off of the surface of annulus 31 before a natural current zero. Thus, low current arcs are extinguished before they can reach the arc-running surface 32. Only those arcs carrying peak values of arcing current in excess of several hundred amperes are driven radially outward sufiiciently to locate one of their terminals on the arcrunning surface 32. The importance of these relationships will be brought out in connection with the following discussion of the chopping phenomena which occurs in avacuum-type interrupter.

As has been mentioned hereinabove, vacuum circuit interrupters for alternating currents have a tendency during low current interruptions to chop, i.e., to drive the current abruptly and prematurely to Zero before a natural current zero is reached. This chopping action is illustrated in FIG. 4, where the current flowing between the contacts is plotted against time. It can be assumed that the contacts are parted to establish an are at an instant such as depicted at B. The are is maintained up until about the instant O, and hence, the current is free to follow substantially its natural curve up until this instant. At the instant 0, however, the current is forced abruptly and prematurely to zero before the natural current zero is reached. It is this action which is referred to throughout this application as chopping. The amount of current chopped is designated 1 and this quantity is referred to hereinafter as the chopping current.

As has been pointed out in the aforementioned Lee et al. Patent No. 2,975,256, this chopping current depends upon the particular contact material being utilized and may vary somewhat from one low current interruption to the next. Typically, however, if an extended number of low current interruptions of less than 50 amperes are performed with a particular contact material, assuming the contact material is free of contaminants, nearly all of the chopping currents encountered will be within about 39% of an average value. The maximum value that ordinarily will be encountered during such low current interruptions we refer to as the representative maximum value. In the disclosed interrupter, the annulus 31 is formed from a material which has a representative maximum currentchopping level below the maximum value which can be tolerated in the inductive circuit to which the interrupter is to be applied. The arc-running surface 32 of the contact is formed of a dissimilar metal which is particularly suited for high current interruptions and which might have a considerably higher representative maximum current chopping level than the material of the annulus 31.

The fact that the arc running-surface 32 is formed of a material that, under low current conditions, might have a relatively high current chopping level is not a significant disadvantage in the interrupter of our invention because we exclude the terminals of substantially all low current arcs from the arc-running surface 32. As was pointed out hereinabove, these low current arcs are maintained on the annulus 31 and only those arcs carrying a peak arcing current in excess of several hundred amperes are driven onto the arc-running surface 32. Chopping is not a significant problem with this latter class of arcs inasmuch as chopping is a phenomenon confined to low current arcs. Hence, those arcs which do reach the arcrunning surface 32 will not produce significant chopping because of their high currents.

The precise current level above which chopping ceases to be a problem varies from one material to the next and varies also with the type of circuit application involved. For most contact materials, however, no significant amount of chopping is encountered for are in which the peak arcing current is above about 500 amperes. Thus, in a preferred form of our invention, we proportion the inner and outer diameters of the annulus 31 in such a manner that the loop circuit L is capable of driving only those arcs with peak currents above about 500 amperes onto the arc-running surface 32. It is realized that arcs having peak currents below 500 amperes (for example, in the range of 200 to 500 amperes) might also involve relatively low current chopping levels, but designing for 500 amperes provides a desirable margin of safety which assures that all arcs below about 200 amperes are interrupted on the annulus 31. It should be understood that, generally speaking, no significant dis-advantage is involved in interrupting 200 to 500 ampere arcs on the annulus 31 inasmuch as such arcs are relatively easy to interrupt and can be interrupted on the material of the annulus 31 without difficulty. As a matter of fact, arcs of a considerably higher peak current than 500 amperes can be interrupted without difficulty on many materials having low current chopping levels, and, accordingly, no serious problem will result even if, by chance, arcs with peak current values above 500 amperes remain behind on the annulus 31. The feature of primary importance is that substantially all arcs with peak currents low enough to produce objectionable levels of chopping if interrupted on the material of the arc-running surface 32 are interrupted with their terminals on the annulus 31 rather than on the arc-running surface 32.

The aforementioned Leet et al. patent sets forth certain criteria which can be utilized for selecting an ap propriate material for the annulus 31. For example, it is pointed out in the Lee et al. application that the choppingcurrent level can consistently be held to on more than four amperes if the material of the arcing region 1) has a low chemical atfinity for oxygen in comparison to that of aluminum, magnesium, and calcium (2) is free of sorbed gases and contaminants, and (3) comprises a metal having a vapor pressure at least equal to that of tin at temperatures exceeding 2000" K. and a thermal conductivity less than that of copper and silver if the metal is one having cahracteristic vapor pressures generally equalling or lower than those of silver for given temperatures.

It is unnecessary that the material be composed entirely of a metal meeting the above requirements. An alloy or mixture containing such a metal is adequate providing the metal is present in suflicient proportions to consistently hold the current-chopping level to the acceptable maximum value, which in the assumed case is for amperes. In other cases, the acceptable level may be either higher or lower.

With reference to the requirement that the material be free of sorbed gases and contaminants, the extent of such freedom should be such that if the material is placed in a vacuumized test chamber a few litres in volume and then deeply eroded by repeated electric arcing, the pressure level in the chamber a few cycles after arcing will remain at least as low as its initial value, even in the absence of getters and pumps and even if the initial pressure in the chamber is on the order of l() m. of mercury.

If the maximum permissible chopping level is lower than four amperes and is as low as say, two amperes, then acceptable chopping performance can be obtained by utilizing for the arcing region a material which meets all of the above requirements and which in addition contains as its high vapor pressure metal constituent a metal having characteristic vapor pressures at least as great as those of lead. If this high vapor pressure metal is combined or alloyed with some other metal, the high vapor pressure metal should be present in suflicient proportions to consistently hold the current-chopping level to the acceptable maximum value, which in this assumed case is two amperes.

In accordance with the above criteria, a suitable material than can be used for the annulus 31 is a mixture of bismuth and copper. In this regard, a mixture of 20% bismuth and copper, by weight, has provided representative maximum chopping levels of less than 2 amperes. This material can therefore be used in those circuit applications where the maximum permissible chopping current is 2 amperes. Contacts of tin have provided maximum representative chopping levels of under three amperes, and the annulus 31 could therefore be formed of tin in those interrupters which are to be applied in circuits where the permissible chopping level is 4 or even 3 amperes. A refractory sponge formed, for example, of tungsten, molybdenum, or carbides of these metals, and impregnated with tin or antimony likewise will provide satisfactory performance in those circuit applications where the maximum permissible chopping level is 4 or even 3 amperes. Other materials having low current chopping levels which are suitable for the annulus 33. are disclosed in the aforementioned Lee et a1. patent. In interrupters that have an interrupting rating not appreciably about 6000 amperes, the annulus 31 can advantageously be formed from a refractory metal or compound thereof (eg. tungsten, molybdenum, or carbides thereof) in combination with one or more of the above described high vapor pressure constituents. Such materials are desirable in that they have a high resistance to contact welding and good mechanical strength. The high vapor pressure constituent must be present, however, or else the chopping level will be intolerably high in view of the fact that refractory metals have typical chopping levels ranging from about 10 amperes to 40 amperes when used alone.

Although many of the materials that have low currentchopping levels are satisfactory for interrupting highcurrent arcs, we prefer to form the arc-running surface 32 from a material which is more ideally suited for high current interruptions. An example of a preferred material is pure copper. Pure copper has a higher current interrupting capacity than most materials which have a lower current-chopping level, evolves less vapors in response to high current arcs and is less expensive and mechanically stronger than most such materials. The maximum representative choping level of copper is about 6 amperes, but this is not a significant disadvantage even in applications where the permissible chopping current is less than 6 amperes because low current arcs will be excluded from the arc-running surface 32, as previously T? explained. Those arcs which do reach the copper arcrunning surface 32 are of such a high current value that little or no chopping is encountered as a result of interruptions on the copper area.

For interrupters which are intended to interrupt currents in excess of 5,000 amperes, the arc-running surface 32 should be formed of a material which is substantially free of refractory constituents such as tungsten, molybdenum, or carbides thereof. For low currents, e.g., less than 500 amperes, the chopping performance of the refractory metals impregnated with high vapor pressure constituents is similar to that of the high vapor pressure constituent when used alone. Thus, such composite materials are capable of maintaining relatively low chopping levels and are satisfactory for the annulus 31. But for high current arcs, e.g. above 2000 amperes, the interrupting performance of such materials is similar to that of the refractory component. Refractory metals tend to thermionically emit even after a current zero is reached when subjected to'the temperatures accompanying such high current arcs, and such emissioninterferes' with the ability of the vacuum to recover its dielectric strength after a current zero. 7 Thus, for the arc-running surface 32, which is exposed to such high current arcs, it is preferable to utilize a material which is substantially free of refractory constituents.

The region of the contact which contains the arc-running surface '32 should also be free of sorbed gases and contaminates and preferably at least to the same extent as described in connection with the annulus 31. If such gases or contaminants were present, they could be evolved during high current interruptions and would thus be present to impair the dielectric strength of the vacuum at the very instant when maximum dielectric recovery would be needed in order to prevent arc-reestablishment after a current zero.

The interruption of heavy current arcs can be facilitated by moving the terminals of the arc at high'speed along the surfaces of the electrode or contact. Such movement tends to minimize the amount of metallic vapors generated from the electrodes by the arc and tends also to increase the degree of diffusion of the vapors that are generated. These factors enable the vacuum to recover its dielectric strength at an increased rate after a current zero and thus render the vacuum more capable of preventing reestablishment of the arc during this critical interval.

For driving the terminals of heavy current arcs about the arc-running surface 32 so as to facilitate interruption thereof, we provide each of the contacts 17 and 18 with slots 34 extending from the outer periphery'of each dish inward. These slots collectively divide each of the contact disks into a series of discrete segments 35 angularly spaced around the contact making region 30. In the preferred form of my invention illustrated in FIGS. 2 and 3, these slots 34 are shown as being of a generally spiral configuration terminating in a mouth 37 at the disk periphery. Each slot extends from its mouth 3'7 in a generally tangential direction with respect to the periphery and terminates only after extending at least to a point near the angular position of the mouth of an adjacent slot. Preferably, the adjacent slots angularl overlap each other as is shown in FIGS.'2 and 3. A slotted construction of this nature is disclosed and claimed in application S.N. 730,413, Schneider, now Patent No. 2,949,520, filed April 23, 1958, and assigned to the assignee of the present invention.

When an are that has been initiated on the contact-making regions Sit is driven outwardly sufiiciently to reach the outer peripheral region of the contacts, each of its terminals is located on one of the segments 36. A typical position of the lower arc terminal is shown for example in FIG. 2 where the arc is designated 33. Considering first the lower contact 18, it will be apparent that because of the slots 34, substantially all of the current flowing between the conductor 13a andthe arc terminal is concentrated in that particular segment 36 which is then carrying the arc terminal. Because of the generally spiral configuration of the slots 34, this current is required to follow a path which is, to an effective extent, tangential with respect to periphery of the disk in theregion of the arc,

as is illustrated by the dotted lines of FIG. 2. As a re sult of this tangential configuration of the current path, the magnetic loop has developed a net tangential force component. This net tangential force component drives the arc in an angular, or circumferential, direction, about the contact, causing it to move to the end of the segment 36 and to jump across the slot 34 to the next segment 36. The current flow to the arc is then concentrated in this next segment, and because of the configuration of this segment, there is a new tangentially acting loop which continues motion of the arc around the contactperiphery. For each of the segments 36, there is a net tangential force component on the are acting in the same angular direction, and, as a result, circumferential motion of the arc continues at high speed until the arc is finally extin- 'guished.

Although we prefer to rely upon slots of the general nature shown at 34 for propelling the are about the arcrunning surface, it is to be understood that the other slot configurations could alternatively be used for achieving the same result. Examples of such other configurations are shown and claimed in the aforementioned Schneider application. Similarly, the desired arc rotation could alternatively be accomplished by relying uponan arcrotating coil for generating a radial magnetic field for reaction with the magnetic field around the arc, as is shown, for example, in US. Patent No. 2,027,836, Rankin et al., assigned to the assignee of the present invention.

lnterrupters' of the type shown in FIG. 1 have been utilized for interrupting arcs having peak currents up to and exceeding 10,000 amperes. When interrupting arcs above a few thousand amperes, the magnetic effect of the loop circuit L is sufiiciently strong to drive the arc terminals on to the arc-runningsurfaces 32 early enough during the arcing interval to assure that the arc terminals will be positioned on the arc-running surfaces during the major portion of the arcing period,

in addition to the current-chopping problem, another troublesome problem in the vacuum interrupter field is that of preventing the contacts from welding together with excessively strong welds, particularly when closing against high currents. This contact=welding problem is particularly troublesome in a vacuum interrupter because the clean surface conditions required for the contacts are ideal for the production of objectionable weld-s. We overcome this contact-welding problem by utilizing for our contact-making annuli 31 a material that has a high resistance to weld-ing under the conditions accompanying closing. One example of such material'is the copper-bismuth alloy mentioned hereinabove. Other examples are alloys of copper and lead and alloys of copper and 'tel luri m, such as are disclosed and claimed in application S.N. 151,552, Lafierty et al., filed November 10, 1961, and assigned to the'assignee of the present invention.

1 These particular weld-resistant materials and the others disclosed and claimed in the Lafferty et al. application each consists essentially of a non-refractory metal major constituent and a non-refractory metal minor constituent, with the minor constituent being highly dispersed throughout the material. The minor constituent has a freezing temperature below that of the major constituent, is soluble in the liquid state in the major constituent to a greater extent than 1% by weight and has a solid state solubility in the major constituent of less than 1% by weight.

Even though the particular weld-resistant alloy for the annulus 31 may be capable'of limiting the chopping level to a value only about the same as that obtainable with pure copper, such chopping levels are satisfactory for certain inductive circuit applications. For example, with the copper base alloys containing only fractional percentages of the high vapor pressure secondary constitu ent, the chopping level can be held to about 6 amperes. Although this is about the same as the maximum representative chopping level for copper, it is well below the 10 to 40 anipe-res resulting from the use of refractory contacts and is satisfactory for many inductive circuits, particuarly in the high voltage range of 7.2 kv. and over.

The arc-running region 32 of such contacts is preferably formed from a conductive material different from that used for the annulus 3'1 and more suited for use in the arc-running region. For example, the pure copper mentioned hereinabove is a preferred material that has a high current interrupting capacity (at least as high as that of the material of the annulus 31), evolves a smaller quantity of vapors than high vapor pressure materials such as bismuth and lead, and is mechanically stronger than certain of the weld-resistant alloys used for annulus 3 1, e.g., copper-bismuth. The superior mechanical strength of the copper enables the slots 34 to be cut in the arcrunn-ing region without causing fracture or undue weakening of this region. As compared to copper bismuth, copper has much more ductility, is much less brittle, and has a higher tensile strength. It is these properties that are being referred to in our statement that copper has superior mechanical strength.

As pointed out here-inabove, the material of the arcrunning region 32 should be devoid of refractory sub stances since these substances cause thermionic emission during a current zero immediately following heavy-current arcing. Such thermionic emission impairs the current-interrupting ability of the interrupter. Although high current arcs are interrupted primarily on the arerunning surface 3 2, it has been found that the presence of refractory substances even in the annulus 31 can de tract from the current-interrupting ability of the interrupter. Although this effect is less pronounced than when the refractory material is in the arc-running surface, it is nevertheless of importance. Thus, in a preferred form of our invention, we use for the annulus 31, as well as for the arc-running region 32, a material devoid of refractoiy constituents that will significantly thermionically emit after a current Zero immediately following several thousand amperes of arcing.

FIGS. 5 and 6 illustrate another embodiment of our invention. This embodiment is similar to that of FIGS. 13, and similar parts have therefore been designated with corresponding reference numerals. The embodiment of FIGS. 5 and 6 differs from that of FIGS. 1-3 in that each of the contacts is formed, not as a complete disk, but only as a segment of a disk, or as a block, extending radially from the arc init-iati-on region in only one general direction. All arcs are initiated on a first electrode region 50 and are driven outwardly toward a second electrode region 53 by the magnetic effect of a loop circuit L correspondingto the similarly-designated loop circuit of FIG. 1. The first electrode region is formed of a material having a lower current-chopping level than the material of the second electrode region, but the material of the second electrode region is more suitable for interrupting high currents. The magnetic effect of the loop circuit L is insufficient to drive arcs of less than several hundred amperes peak current off of the first electrode region 50 but is suficient to drive arcs having a peak current exceeding about 500 amperes off of its first electrode region 50 onto the second electrode region 53. Thus, low current arcs which might produce objectionable chopping if interrupted on the material of electrode region 5 3 are excluded from region 53 and are interrupted on region 59 where the resu'lant chopping is under the acceptable maximum. High current arc-s are interrupted on the second electrode region 53 and in most cases are positioned on the second electrode region during the major portion of 10 the arcing interval. The same materials as are used for the annulus 31 and the arc-running surface 32 of the interrupter of FIG. 1 can be used for the regions 50 and 53, respectively, of the interrupter of FIGS. 5 through 6. The insert forming each electrode region 50 is brazed to the remainder of its contact only along the portion of its back surface radially aligned with the contact-making area of the region 56, for reasons corresponding to those described relative to FIG. 1a.

Although the interrupter of FIGS. 5 through 6 has no means for rotating an are, as is the case with the interrupter of FIG. 1, some desirable motion of the arc is effected by driving the arc terminals radially outward along the arc-running surface 53. The arrangement of FIG. 5' is therefore usable where lower speeds of arc motion can be tolerated.

In the two embodiments shown in FIG. 1 and FIG. 5,

the juxtaposed electrode of each contact region, e.g. the regions 50 and 53 of FIG. 5, are integrally joined together. It should be understood, however, that our invention is not limited to such integrally-constructed contacts. It is equally applicable, for example, to an arrangement in which the electrode regions of one of the contacts are relatively movable. Such an arrangement is depicted in FIG. 7, where reference numerals corresponding to those of FIG. 5 are used to designate corresponding parts. The lower contact of FIG. 7 comprises a movable rod 18a to which is attached the first electrode region 50. This rod 18a, which is shown in its open-circuit position, can be driven upwardly to effect engagement between the electrode regions 50 of the upper and lower contacts, thereby closing the interrupter. Opening is effected by driving the rod 18a downwardly into its position of FIG. 7. The arc-running region 53 of the lower contact, instead of being integral with the contact-making region 50, is formed on a stationary conductive part 60 which remains fixed while the contact-making region 50 is moved through opening and closing operations. During a circuit-opening operation, lower terminal for a heavy current are is driven from the first electrode region 50 onto the second electrode region 53 in substantially the same manner as described hereinabove in connection with FIGS. 1 and 5. Low current arcs are excluded from the electrode region 53 in substantially the same manner as described hereinabove in connection with FIGS. 1 and 5. The stationary part 6!) is preferably integrally joined to the lower end cap 13 and, in this way, is electrically connected to the contact rod 18a. The same materials as are used for the annulus 31 and the arc-running surface 32 of the interrupter of FIG. 1 can be used for the regions 50 and 53, respectively, of FIG. 7.

Although we prefer to form both of the two mating contacts from the same combination of materials, We wish it to be understood that our invention is not limited to such an arrangement. As one example illustrative of how the interrupter of FIG. 1 could be modified in this regard, the electrode region 30, 30a of one contact could be formed of one particular material having a low currentchopping level and the electrode region 30, 30a of the other or mating contact could be formed of some different material which also has a low current-chopping level. As another example, in some circuit applications, it is sufficient if only one of the contacts 17, 18 be provided with an annulus of low current-chopping material, with the other contact being formed over its entire arcing surface of the same material as is used for its arc-running surface, e.g. copper. With regard to this latter type of arrangement, it is significant to note that chopping appears to be a phenomena initiated primarily at the cathode. If it can be predetermined which of the two electrodes will serve as the cathode during low current interruptions, then this electrode alone can be provided with the annulus of low current-chopping material.

Where very short arcing gaps are relied upon, it is suificient if only the anode material has low currentchopping characteristics. Where the gap is short, the anode material alone will provide the vapor supply required to hold the chopping current to a level approaching that characteristic of the material when used as a cathode. In such applications, it will therefore be apparent that either of the two electrodes can be provided with the annulus of low curren -chopping material.

For protecting the insulation of a vacuum-type interrupter from the build-up of a metallic coating thereon, it is customary to provide a vapor-condensing shield between the arcing gap of the interrupter and the protected insulating surface. The interrupter of this application employs such a shield for protecting the internal surface of insulating casing 11, but for the sake of simplification, we have omitted such shield from the drawing. For a detailed example of a suitable shield for protecting the casing 11, reference may be had to applicaiton S.N. 630,247, Crouch, now Patent No. 2,892,911, filed December 24, 1956, and assigned to the assignee of the present invention. The shield of the Crouch application comprises a metallic tube surrounding the arcing gap and electrically isolated from both electrodes. 7

While we have shown and described particular embodiments'of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a vacuum-type circuit interrupter, an envelope evacuated to at least about l mm. of mercury, a pair of separable electrodes disposed within said envelope, one of said electrodes comprising juxtaposed first and second electrode regions formed of dissimilar conductive materials, the material of said first region having a substantially lower maximum representative current-chopping level than the material of said second region, arc-initiating means for initiating substantially all circuit interrupting arcs within said envelope in a location wherein one are terminal is located on said first electrode region at the instant of arc-initiation, said arc-initiating means comprising means for causing final parting of said electrodes during an interrupting operation to occur on said first electrode region, magnetic means for driving arcs from the location where said arcs are initiated onto said second electrode region, means for maintaining the terminal of low current arcs on said first electrode region until arcextinction comprising a surface area of said first electrode region interposed between all arc-initiating locations and said second electrode region, said magnetic means driving high current arcs from said first electrode region onto said second electrode region at a speed sufiiciently high to locate the arc terminal of said high current arcs on said second region during a major portion of the arcing interval, said magnetic means having insuificient arcmotivating ability during low current interruptions to drive .the terminal of low current arcs off of said first electrode region before arc-extinction.

2. In a vacuum-type circuit interrupter, an envelope evacuated to at least about mm. of mercury, a pair of separable electrodes disposed within said envelope, one of said electrodes comprising juxtaposed first and second electrode regions formed of dissimilar conductive materials, the material of said first region having'a substantially lower maximum representative current-chopping level than the material of said second region, arc-initiating means for initiating substantially all circuit-interrupting arcs within said envelope in a location wherein one arc terminal is located on said first electrode region at the time of arc-initiation, said arc-initiating means comprising means for causing final parting of said electrodes during E2 from their initiation point toward said second electrode region with a speed varying directly in accordance with the current being interrupted, means for maintaining the terminal of all arcs below several hundred amperes on said first electrode region until arc-extinction comprising a surface area of said first electrode region interposed between all arc-initiating locations and said second electrode region, said magnetic means acting to drive only those arcs above several hundred amperes at a speed suficient to locate one are terminal of said latter arcs on said second region before arc-extinction, said magnetic means having insulficient arc-motivating ability during low current interruptions to drive the terminal of low current arcs oil of said first electrode region before arc-extinction.

V 3. In a vacuum-type circuit interrupter, an envelope evacuated to at least 10' mm. of mercury, a pair of coacting contacts disposed Within said envelope and relatively movable from a position of engagement to a position of disengagement to establish a circuit-interrupting are between said contacts, at least one .of said contacts comprising disk-shaped structure of conductive material having a major surface facing the other of said contacts, a conductor connected to said disk-shaped structure generally centrally thereof for carrying current to and from said disk-shaped structure, said major surface having a generally centrally-located region which is disposed out of engagement with said other contact even when said contacts are engaged, said major surface further comprising a low-current arcing area surrounding said central region and including a contact-making area for engaging said other contact when said contacts are in engagement, means for causing said contacts to finally part on said contact-making area during a contact-disengaging operation to initiate circuit-interrupting arcs thereon, said contact making area being so located as to provide a radially-outwardly-acting loop circuit for current flowing between said conductor and said contact-making area, said major surface also including a high-current arcing area surrounding said low-current arcing area and adapted to receive a terminal of arcs driven radially outwardly off of said low-current arcing area by said loop circuit upon contact disengagement, said low-current arcing 'area and said high-current arcing area being formed of dissimilar I conductive materials, the material of said low-current arcing area having a substantially lower maximum representative current-chopping level than the material of said high-current arcing area, said low-current arcing area extending radially outward by a sufiicient amount to maintain the terminal of all low-current arcs on said lowcurrent arcing area until arc-extinction, the radially outwardly acting magnetic effect of said loop circuit being suificient to drive only those arcs above several hundred amperes onto said high-current arcing area.

4. The vacuum-type circuit interrupter of claim 3 in combination with means for impelling the arc terminal of high-current arcs about the outer peripheral portion of said major surface once'the arc terminal has moved on to said high-current arcing region. 7

5. The interrupter of claim 3 in which said one contact comprises a body portion and an annulus having one lateral face defining said contact-making area and a second lateral face adapted to be joined to said body portion, and means including a brazed joint between said second face and said body portion located at least partially in radial alignment with said contact-making area for causing the current path for the major portion of the current to be devoid of any radially-inwardly bowed loop portions in the region leading from the contact-making area through the annulus.

6. In a vacuum-type circuit interrupter, an envelope evacuated to at least about 10- mm. of mercury, a pair of separable electrodes disposed within said envelope, one of said electrodes comprising juxtaposed first and second electrode regions formed of dissimilar conductive materials, the material of said first region having a substantially lower current-chopping level than the material of said second region and being capable of consistently holding the chopping level below four amperes, arc-initiating means for initiating substantially all circuit-interrupting arcs within said envelope in a location wherein one are terminal is located on saidfirst electrode region at the instant of arc-initiation, said arcinitiating means comprising means for causing final parting of said electrodes during an interrupting operation to occur on said first electrode region, magnetic means for driving circuit interrupting arcs from their initiation point toward said second electrode region with a speed varying directly in accordance with the current being interrupted, means for maintaining on said first electrode region until arc-extinction the terminal of all arcs having a current content below a value that would produce greater than four amperes of chopping if interrupted on the material of said second electrode region, said latter means comprising a surface area of said first electrode region interposed between all arc-initiating locations and said second electrode region, said magnetic means acting to drive onto said second electrode region the terminal of only those arcs having a current content above said value, said magnetic means having insufiicient arc-motivating ability during low-current interruptions to drive the terminal of an are having a current content below said value off of said first electrode region before are extinction.

7. In a vacuum-type circuit interrupter, an envelope evacuated to at least about 10 mm. of mercury, a pair of separable electrodes disposed within said envelope, one of said electrodes comprising juxtaposed first and second electrode regions formed of dissimilar conductive materials, the material of said first region having a substantially lower. current-chopping level than the mate rial of said second region and being capable of consistently holding the chopping level below two amperes, arcinitiating means for initiating substantially all circuitinterrupting arcs within said envelope in a location wherein one are terminal is located on said first electrode region at the instant of arc-initiation, said arc-initiating means comprising means for causing final parting of said electrodes during an interrupting operation to occur on said first electrode region, magnetic means for driving circuit-interrupting arcs from their initiation point toward said second electrode region with a speed varying directly in accordance with the current being interrupted, means for maintaining on said first electrode region until arc-extinction the terminal of all arcs having a current content below a value that would produce greater than two amperes of chopping if interrupted on the material of said second electrode region, said latter means comprising a surface area of said first electrode region interposed between allarc-initiating locations and said second electrode region, said magnetic means acting to drive onto said second electrode region the terminal of only those arcs having a current content above said value, said magnetic means having insutficient arc-motivating ability during low current interruptions to drive the terminal of an are having a current content below said value oil? of said first electrode region before arc-extinction.

8. The interrupter of claim 6 in which said first electrode region is free of sorbed gases and contaminants to such an extent that if placed in a vacuumized test chamber a few litres in volume and then deeply eroded by repeated electric arcing, the pressure level in said test chamber a few cycles after arcing will remain substantially as low as its initial value, even in the absence of gctters and pumps and even if the initial pressure in the test chamber is on the order of 10" mm. of mercury; said first electrode region being formed of a material having a vapor pressure less than mm. of mercury at 500 K.; said material comprising a metal having a vapor pressure at least as great as that of tin at temperatures exceeding 2000 K.; said metal being present in sufficient quantity to consistently hold the choppingcurrent level to no greater than four amperes when arcs of less than 50 amperes peak current are interrupted on said first electrode region; said metal having a thermal conductivity substantially less than that of copper and silver if the metal is one having characteristic vapor pressures generally equalling or lower than those of silver for given temperatures; the chemical afimity of said material for oxygen being relatively low as compared to that of aluminum, magnesium, and calrum 9. The interrupter of claim 7 in which said first electrode region is free of sorbed gases and contaminants to such an extent that if placed in a vacuumized test chamber a few litres in volume and then deeply eroded by repeated electric arcing, the pressure level in said test chamber a few cycles after arcing will remain substantially as low as its initial value, even in the absence of getters and pumps and even if the initial pressure in the test chamber is on the order of 10* mm. of mercury; said first electrode region being formed of a material having a vapor pressure less than 10- mm. of mercury at 500 K.; said material comprising a metal having characteristic vapor pressures at least as great as those of lead in a sufiicient quantity to consistently hold the chopping-current level to no more than two amperes when arcs of less than 50 amperes peak current are interrupted on said first electrode region; the chemical afiinity of said material for oxygen being relatively low as compared to that of aluminum, magnesium, and cal- Clllm.

10. The interrupter of claim 1 in which said second electrode region is formed of a material having a higher current interrupting capacity than the material of said first electrode region when interrupting currents above 2000 amperes.

11. The interrupter of claim 1 in which said second electrode region is formed of a material having a higher current interrupting capacity than the material of said first electrode region, the material of said second electrode region being substantially free of refractory metallic substances that significantly thermionically emit after a current zero is reached following several thousand amperes of arcing current.

12. The interrupter of claim 3 in which said high current arcing area is formed of a material having a higher current interrupting capacity than the material of said low current arcing area, the material of said high current arcing area being substantially free of refractory metallic substances that significantly thermionically emit after a current Zero is reached following several thousand amperes of arcing current.

13. In a vacuum type circuit interrupter, an envelope evacuated to at least 10* mm. of mercury, a pair of electrode structures disposed within said envelope, one of said electrode structures comprising juxtaposed first and second regions of dissimilar conductive materials that are substantially free of sorbed gases, said first region being movable into engagement with the other of said electrode structures to make the circuit through said interrupter and being movable out of engagement with said other electrode structure to initiate substantially all circuit-interrupting arcs in a location wherein one are terminal is located on said first region at the instant of arc-initiation, final parting of said electrode structures when moved out of engagement occurring on said first electrode region, the material of said first region being an alloy comprising a non-refractory metal major constituent and a non-refractory metal minor constituent, the minor constituent having a freezing temperature below that of the major constituent, the minor constituent having a lquid state solubility in the major constituent greater than 1% by weight and a solid state solubility less than 1% by weight, the material of said second region being a metal that is more ductile and has a higher arsarae tensile strength than said first material and that isdevoid of refractory metallic substances that significantly thermionically emit after a current zero immediately following several thousand amperes of arcing, the material of said second region having a current interruputing ability at least as high as the material of said first region,magnetic means for driving high current arcs from said first electrode region on to said second electrode region at a speed sufficiently high to locate the arc terminal of said high current arcs on said second region during a major portion of the arcing interval, and means including slots in said second region for developing magnetic forces for controlling arc-motion on said second region.

14. The vacuum type circuit interrupter of claim 13 in which both said first and second electrode regions are free of refractory metallic substances which significantly thermionically emit after a current zero is reached immediately following several thousand amperes of arcing.

15. The interrupter of claim 13 in which the material of said first region is an'alloy of copper and bismuth and the material of said second region is copper.

16. In a vacuum-type circuit interrupter, an envelope evacuated to at least mm. of mercury, a pair of coacting contacts disposed within said envelope and relatively movable from a position of engagement to a position of disengagement to establish a circuit-interrupting are between said contacts, at least one of said contacts comprising disk-shaped structure of conductive material having a major surface facing the other of said contacts, a conductor connected to said disk-shapedstructure generally centrally thereof for carrying current to and from said disk-shaped structure, said major surface having a generally centrally-located region which is disposed out of engagement with said other contact even when said contacts are engaged, said major surface further comprising a low-current arcing area surrounding said central region and including a contact-making area for engaging said other contact when said contacts are in engagement, said contact-making area being so located as to provide a radially-outwardly-acting loop circuit 'for current flowing between said conductor and said contact-making area, means for causing final parting of said contacts during an interrupting operation to occur on said contact-making area, said major surface also including a high-current arcing area surrounding said low-current arcing area and adapted to receive a terminal of arcs driven radially outwardly off said low-current arcing area by said loop'circuit upon contact disengagement, said low-current arcing area and said high-current arcing area being formed of dissimilar conductive materials that are substantially free of sorbed gases, the material of said low current arcing area being an alloy comprising a nonrefractory metal major constituent and a non-refractory metal minor constituent, the minor constituent having a freezing temperature below that of the major constituent, the minor constituent having a liquid state solubility in the major constituent greater than 1% by weight and a solid state solubility in the major constituent less than 1% by weight, the material of said high current arcing area being a metal that is more ductile and has a higher tensile strength than said first material and that is devoid of refractory metallic substances that significantly thermionically emit after a current Zero immediately following several thousand amperes of arcing, the material of said high currentarcing area having a current interrupting ability at least as high as the material of said low current arcing area.

17. The vacuum type circuit interrupter or" claim 16 in which both said low current arcing area and said high current arcing area are free of refractory metallic substances that significantly thermionically. emit after a current zero is reached immediately following several thousand amperes of arcing.

18. The interrupter of claim 1 in which said magnetic means comprises a radially-outwardly acting loop circuit and in which said first electrode region includes a contact-making area, said electrode structure comprising a body portion and an insert having one lateral face defining said contact-making area and a second lateral face adapted to be joined to said body portion, and means including a brazed jointtbetween said second face and said body portion .atleast partially in radial alignment with said contact-making area for causing, the current path for the major portion ofthe current leading from the contact-making area through the insert to be devoid of any radially-inwardly bowed loop portions.

7 References Cited in the file of this patent UNITED STATES PATENTS 7 2,575,730 Sandin et al. Nov. 20, 1951 2,900,476 Reece Aug. 18, 1959 2,949,520 Schneider Aug. 16, 1960 2,975,255 Lafierty Mar. 14, 1961 2,975,256 Lee et al. Mar. 14, 1961 3,016,436 Laiferty Jan. 9, 1962 FOREIGN PATENTS 259,029 Italy June 13, 1928 709,005 France May 11, 1931 Great Britain Dec. 

1. IN A VACUUM-TYPE CIRCUIT INTERRUPTER, AN ENVELOPE EVACUATED TO AT LEAST ABOUT 10-4 MM. OF MERCURY, A PAIR OF SEPARABLE ELECTRODES DISPOSED WITHIN SAID ENVELOPE, ONE OF SAID ELECTRODES COMPRISING JUXTAPOSED FIRST AND SECOND ELECTRODE REGIONS FORMED OF DISSIMILAR CONDUCTIVE MATERIALS, THE MATERIAL OF SAID FIRST REGION HAVING A SUBSTANTIALLY LOWER MAXIMUM REPRESENTATIVE CURRENT-CHOPPING LEVEL THAN THE MATERIAL OF SAID SECOND REGION, ARC-INITIATING MEANS FOR INITIATING SUBSTANTIALLY ALL CIRCUIT-INTERRUPTING ARCS WITHIN SAID ENVELOPE IN A LOCATION WHEREIN ONE ARC TERMINAL IS LOCATED ON SAID FIRST ELECTRODE REGION AT THE INSTANT OF ARC-INITIATION, SAID ARC-INITIATING MEANS COMPRISING MEANS FOR CAUSING FINAL PARTING OF SAID ELECTRODES DURING AN INTERRUPTING OPERATION TO OCCUR ON SAID FIRST ELECTRODE REGION, MAGNETIC MEANS FOR DRIVING ARCS FROM THE LOCATION WHERE SAID ARCS ARE INITIATED ONTO SAID SECOND ELECTRODE REGION, MEANS FOR MAINTAINING THE TERMINAL OF LOW CURRENT ARCS ON SAID FIRST ELECTRODE REGION UNTIL ARCEXTINCTION COMPRISING A SURFACE AREA OF SAID FIRST ELECTRODE REGION INTERPOSED BETWEEN ALL ARC-INITIATING LOCATIONS AND SAID SECOND ELECTRODE REGION, SAID MAGNETIC MEANS DRIVING HIGH CURRENT ARCS FROM SAID FIRST ELECTRODE REGION ONTO SAID SECOND ELECTRODE REGION AT A SPEED SUFFICIENTLY HIGH TO LOCATED THE ARC TERMINAL OF SAID HIGH CURRENT ARCS ON SAID SECOND REGION DURING A MAJOR PORTION OF THE ARCING INTERVAL, SAID MAGNETIC MEANS HAVING INSUFFICIENT ARCMOTIVATING ABILITY DURING LOW CURRENT INTERRUPTIONS TO DRIVE THE TERMINAL OF LOW CURRENT ARCS OFF OF SAID FIRST ELECTRODE REGION BEFORE ARC-EXTINCTION. 